Syn flood to TCP port 21 from priveleged port (80)

Tue Nov 1 19:48:19 UTC 2016

Not sure why reflected RSTs are the goal here, they're not much of an amplification
to the original syn size. Additionally causing a mild dos of my clients' stuff
when it begins throttling # of connections, ie noticeable. (not that i want to
help scriptkids improve their attacks...). Im guessing port 80 was chosen for improved
fw piercing.

Sure is widespread though, 5 clients on very different networks all seeing similar
saturation. Someone has a nice complete prescanned list of open ftps for the
entire internet out there (or are they just saturating the whole /0?)

Easy to filter though:

tcp and src port 80 and src net '(141.138.128.0/21 or 95.131.184.0/21)' and dst port 21

Adapt for your fw rules of choice.

/kc

On Tue, Nov 01, 2016 at 07:39:40PM +0000, Van Dyk, Donovan said:
  >I think Ken has nailed it. I think the source addresses are spoofed so you reflect the connection (tcp syn ack) to those source addresses. Get enough of those connections and the server is dead. 
  >
  >Since your port 21 is open
  >
  >telnet 109.72.248.114 21
  >Trying 109.72.248.114...
  >Connected to 109.72.248.114.
  >Escape character is '^]'.
  >
  >Your address was probably scanned and saw it could be used in the attack.
  >
  >Regards
  >--
  >Donovan Van Dyk
  >
  >SOC Network Engineer
  >
  >Office: +1.954.620.6002 x911
  >
  >Fort Lauderdale, FL USA
  >
  >
  >
  >
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  > 
  >
  >On 11/1/16, 3:29 PM, "Ken Chase" <math at sizone.org> wrote:
  >
  >    seeing an awful lot of port 80 hitting port 21. (Why would port 80
  >    ever be used as source?). Also saw a buncha cpanel "FAILED: FTP" alerts flickering
  >    on and off as the service throttled itself at a couple client sites I manage.
  >    
  >    I see 540 unique source IPs hitting 32 destinations on my network in just 1000
  >    packets dumped on one router. 
  >    
  >    All from multiple sequential registered /24s in whois, but all from one
  >    management company:
  >    
  >    141.138.128.0/21 and 95.131.184.0/21
  >    
  >    role:           William Hill Network Services
  >    abuse-mailbox:  networkservices at williamhill.co.uk
  >    address:        Infrastructure Services 2 City Walk Sweet Street Leeds LS11 9AR
  >    
  >    AS49061
  >    
  >    course, synfloods can be spoofed... perhaps they're hoping for a retaliation
  >    against WHNS.
  >    
  >    /kc
  >    
  >    On Tue, Nov 01, 2016 at 09:44:23PM +0300, Oleg A. Arkhangelsky said:
  >      >Hello,
  >      >
  >      >A couple of cuts from tcpdump output:
  >      >
  >      >21:31:54.995170 IP 141.138.131.115.80 > 109.72.248.114.21: Flags [S], seq 1376379765, win 8192, length 0
  >      >21:31:55.231925 IP 194.73.173.154.80 > 109.72.241.198.21: Flags [S], seq 2254756684, win 8192, length 0
  >      >21:27:50.413927 IP 95.131.188.179.80 > 109.72.248.114.21: Flags [S], seq 3619475318, win 8192, length 0
  >      >21:27:50.477014 IP 95.131.191.77.80 > 109.72.248.114.21: Flags [S], seq 2412690982, win 8192, length 0
  >      >
  >      >Does anyone seeing this right now (18:31 UTC)? I see this traffic
  >      >on at least two completely independent ISPs near Moscow. The
  >      >rate is about a few dozen PPS hitting all BGP-announced networks.
  >      >
  >      >--??
  >      >wbr, Oleg.
  >      >
  >      >"Anarchy is about taking complete responsibility for yourself."
  >      >?? ?? ?? Alan Moore.
  >    
-- 
Ken Chase - math at sizone.org Guelph Canada